1. Field of the Invention
The present invention relates to what is called a front-opening interface mechanical standard (FIMS) system, that is, a load port apparatus, which is used for transferring, from one semiconductor processing apparatus to another semiconductor processing apparatus, wafers held in a sealed-type transport container called a pod, or for transferring the wafers from the semiconductor processing apparatus to the pot, during a semiconductor manufacturing process and the like.
2. Description of the Related Art
In recent years, in a general semiconductor manufacturing process, cleanliness is managed throughout the entire process by maintaining a highly clean state in only the following three spaces: inner spaces of various processing apparatus; an inner space of a pod capable of containing wafers and transporting the wafers from one processing apparatus to another processing apparatus; and a mini-environment in which the wafers are exchanged between the pod and the respective processing apparatus. Such a pod includes a main-unit portion which houses wafers therein and which has a wafer-insertion-and-removal opening formed in one side surface, and a lid which makes the inside of the pod serve as a sealed space by closing the opening. Further, a structure that defines the mini-environment includes an opening portion capable of facing the above-mentioned opening of the pod and a second opening portion arranged on the semiconductor processing apparatus side so as to face the opening portion.
The load port apparatus includes a member as a partition wall provided with the opening portion, that is, a wall called a side base, a door for closing the opening portion, a door drive mechanism for controlling operation of the door, and a mount table on which the pod is to be mounted. The side base partitions and defines the above-mentioned mini-environment. A mount base is capable of supporting the pod in such a manner as to face the opening of the pod and the opening portion each other, and brings the lid of the pod close to or apart from the door together with the pod itself. The door is capable of holding the lid of the pod. The door drive mechanism causes the door to open and close the opening portion under a state of holding the lid, and the door is caused to retract below a space between the opening portion and the second opening portion or to enter the space. A robot is arranged in the mini-environment, and the robot is capable of entering into and retracting from the inside of the pod through the opening portion and the opening of the pod, and transfers wafers between the inside of the pod and the semiconductor processing apparatus also through the second opening portion.
In the semiconductor manufacturing process, the wafers contained in the pod may have, for example, metal wiring formed thereon. Such metal wiring has a risk that, due to surface oxidation thereof, desired characteristics cannot be obtained when a device is completed. Therefore, oxygen concentration in the pod needs to be maintained at a low level. As a technology provided to meet such a demand, Japanese Patent Application Laid-Open No. 2007-180517 discloses a configuration for maintaining the oxygen concentration in the pod at a low level by generating, when the wafers are inserted into and removed from the pod, a gas curtain from an inert gas in parallel to the opening of the pod so as to suppress entrance of an oxidizing gas of the mini-environment into the pod, and by supplying the inert gas directly into the pod. Further, Domestic Re-publication of PCT International Publication No. 2005-124853 discloses a configuration for reducing the oxygen concentration in the pod by generating a space containing an inert gas at high concentration in the periphery of the opening portion of the pod, and in this state, supplying the inert gas into the pod.
The above-mentioned inert gas to be supplied for reducing the oxygen concentration is generally discharged to a space in which the inert gas is sufficiently reduced in concentration via a so-called grating for discharging a gas, which is provided in, for example, a bottom surface of the mini-environment, and further via an inert gas discharge passage. However, the inert gas may stagnate and accumulate in, for example, a region inside the mount table, which is spaced apart from a so-called downflow generated in the mini-environment and from the curtain-like gas flow disclosed in Japanese Patent Application Laid-Open No. 2007-180517 or Domestic Re-publication of PCT International Publication No. 2005-124853. Due to the presence of such a region, an operator's working environment may be deteriorated, but as exemplified in the configurations disclosed in Japanese Patent Application Laid-Open No. 2007-180517 and Domestic Re-publication of PCT International Publication No. 2005-124853, no consideration has conventionally been given for such stagnation of the inert gas.